FIG. 1 illustrates a cross-sectional view of a human eye 10 having an anterior chamber 12 and a posterior chamber 14 separated by an iris 30. Within the posterior chamber 14 is a capsular bag 16 which holds the eye's natural crystalline lens 17. The capsular bag comprises an anterior capsule 16a and a posterior capsule 16b that meet at a capsular rim 16c. Light enters the eye by passing through cornea 18. The cornea and crystalline lens act together to direct and focus the light onto retina 20. The retina is connected to optic nerve 22 which transmits images received by the retina to the brain for interpretation. Eye 10 has a visual axis VA
In an eye where the natural crystalline lens has been damaged (e.g., clouded by cataracts), the natural lens is no longer able to properly focus and/or direct incoming light to the retina. As a result images become blurred. A well known surgical technique to remedy this situation involves removal of a damaged crystalline lens through a hole in the capsular bag known as a capsularhexis (also referred to simply as a rhexis). Subsequently, an artificial lens known as an intraocular lens (IOL) can be placed into the evacuated capsular bag through the rhexis.
Conventional IOLs are typically fixed-focus lenses. Such lenses are usually selected to have an optical power such that the patient has a fixed focus for distance vision, and the patient requires spectacles or contact lenses to permit near vision. In recent years extensive research has been carried out to develop IOLs having variable focus capability. Such IOLs are known as accommodating IOLs (AIOLS). The term “AIOLs” refers to both single-element and multi-element systems.
Single-element AIOLs typically have two or more haptics, each comprising a plate to position the lens in the capsular bag and to mechanically interact with the capsular bag to achieve accommodative movement. For example, the haptics extend generally radially outward from sides of the optic and are movable anteriorly and posteriorly relative to the optic.
In some conventional lens embodiments, the plate haptics are hinged proximate the optic to permit anterior/posterior movement of the optic and haptic. The accommodative movement involves pivotal movement of the haptics at their corresponding hinge and translation of the optic relative to the eye; accordingly, the optic and the haptics undergo accommodative movement. In other conventional embodiments, the plate haptics are resiliently flexible, and the anterior/posterior movement of the haptics relative to the optic involves resilient flexing or bending of the haptics throughout their lengths.
Conventional lenses having plate haptics are constructed and arranged to utilize compression of the capsular rim, the elasticity of the posterior capsule and pressure in the vitreous cavity 19, in combination with the natural brain-controlled ciliary muscle action of the eye to provide postoperative accommodation for near vision. Thus, according to some eye models, when looking at a near object, the brain constricts the ciliary muscle thereby relaxing the fibrosed anterior rim and increasing vitreous cavity pressure in such a way as to effect forward movement of the lens, i.e. accommodation movement of the lens optic along the axis of the eye to a near vision position. Depending upon the amount of accommodation, accommodation deflection of the lens is produced initially by an increase in vitreous pressure due to backward movement of the ciliary muscle into the vitreous body as the muscle contracts thereby causing the vitreous body to bulge forward at its boundary with the capsular bag, and a forward bias force of the stretched posterior capsule and finally by forward movement of the lens. Subsequent brain-activated relaxation of the ciliary muscle causes the capsular bag and the fibrosed anterior capsular rim to return the lens rearward toward its distant vision position.